PyPy is a fast, compliant alternative implementation of the Python language
(equivalent to CPython 2.7.1). It has several advantages and distinct
features:

  Speed: thanks to its Just-in-Time compiler, Python programs often run
    faster on PyPy.
  Memory usage: large, memory-hungry Python programs might end up taking
    less space than they do in CPython.
  Compatibility: PyPy is highly compatible with existing python code. It
    supports ctypes and can run popular python libraries like twisted
    and django.
  Sandboxing: PyPy provides the ability to run untrusted code in a fully
    secure way.
  Stackless: PyPy can be configured to run in stackless mode, providing
    micro-threads for massive concurrency.
